This invention pertains generally to electric circuit breakers and ground fault interrupters and more particularly to a branch circuit breaker having a ground fault interrupter for protecting human life against electrical shock.
Electric circuit breakers of the prior art commonly include means for protecting a circuit against "overcurrent" conditions wherein the current through the breaker is in the order of 125% to 300% of the nominal rating of the breaker and against "short circuit" conditions wherein the current is in excess of approximately 300% of the nominal rating. Such circuit breakers are available in a wide range of physical sizes and current ratings.
Some attempts have heretofore been made to incorporate ground fault protection in some of the larger circuit breakers. Such attempts have included the use of bimetallic strips for detecting an imbalance in the currents to and from a protected circuit and the use of a differential transformer having a plurality of primary windings for detecting the current imbalance and a secondary winding connected directly to a trip coil for actuating the trip mechanism of the breaker. Such techniques are capable of detecting fault currents on the order of 25% of the normal load current, and they therefore provide some protection for property. They, however, are not suitable for protecting human life which requires the detection of fault currents on the order of 3 to 50 milliamperes with load currents ranging on the order of 10 to 100 amperes.
There is, therefore, a need for a new and improved electric circuit breaker which includes means for protecting human life against electrical shock.